1. Field of the Invention
The invention relates to a magnetic circuit device for implementing the magnetic circuit of a magnetic-inductive flow meter, having at least one coil which has a coil core and which generates a magnetic field, with at least two opposing flat pole elements between which, in the installed state of the magnetic circuit device, the measurement tube of the magnetic-inductive flow meter is located in the flow meter, and having at least one magnetically conductive connecting element for magnetic closure of the magnetic circuit. Moreover, the invention also relates to a magnetic-inductive flow meter with at least one measurement tube, with at least one magnetic circuit device for implementing the magnetic circuit and with at least two electrodes for detecting a measurement voltage, the magnetic circuit device having at least one coil which has a coil core and which generates a magnetic field, at least two opposite flat pole elements between which the measurement tube is located, and at least one magnetically conductive connecting element for magnetic closure of the magnetic circuit.
2. Description of Related Art
It is recognized that there are no “open magnetic fields” but only “closed magnetic circuits”. Therefore, by stating that there is at least one magnetically conductive connecting element for magnetic closure of the magnetic circuit, this magnetically conductive connecting element is part of the magnetic circuit, and therefore the part of the magnetic circuit which leads to its actually being a closed magnetic circuit.
Generating a magnetic field in the measurement tube of a magnetic-inductive flow meter is essential for the implementation of the measurement principle which is based on the separation of moving charges in a magnetic field. The measurement engineering basis is formed by a measurement tube of nonmagnetic material, for example, of a nonmagnetic metal which on the flow side is electrically insulated from the measurement fluid by an insulating lining and which is penetrated perpendicular to the flow direction by a magnetic field which has been generated by the coil of the magnetic circuit device. If a measurement fluid with a minimum electrical conductivity flows through the measurement tube, the charge carriers which are present in the conductive measurement fluid are deflected by the magnetic field. On measurement electrodes which are located perpendicular to the magnetic field and to the flow direction, the charge separation yields a potential difference, therefore a voltage which is detected with a measuring instrument and is evaluated as a measurement voltage. The measurement voltage is proportional to the flow velocity of the charge carriers moved with the measurement fluid so that conclusions about the flow rate in the measurement tube can be drawn from the flow velocity.
Magnetic-inductive flow meters have the advantage that they essentially do not intrude into the flow within the measurement tube so that the flow remains undisturbed, the measurement principle easily achieving accuracies in the range of 1% of the measured value, in part even better accuracies can be achieved.
The structure of magnetic-inductive flow meters is however relatively demanding, exactly like the evaluation of the measurement signals so that magnetic-inductive flow meters have not been possible for large-scale applications from a low-cost standpoint, for example, as domestic water meters.
Otherwise, a problem lies in that, to generate a magnetic field which is strong enough for a measurement between the opposite pole elements, electrical power must be continuously made available which has a considerable portion of the electrical power which is altogether necessary for operation of a magnetic-inductive flow meter. For this reason magnetic-inductive mass flow meters which are to be operated free of the power grid (do not have to be “plugged-in,” for example) are difficult to implement, in any case not if maintenance-free operating times of several years are to be implemented.